1. Technical Field of the Invention
The present invention relates to coin (button)-type electric double layer capacitors utilizing a lithium ion-conductive non-aqueous electrolyte and comprising a substance capable of occluding and discharging lithium, metallic lithium, or an alloy thereof as a negative active material, and a substance capable of occluding and discharging lithium as the positive active material. The present invention also relates to an electric double layer capacitor mountable by reflow a soldering and to a method of producing the same.
2. Prior Art
Because coin (button)-type electric double layer capacitors are lightweight and are capable of yielding high energy density, their application to back-up power sources of electric appliances has been increasing.
In case of using the capacitor above mainly as the memory back-up power source, in general, a terminal for use in soldering is welded to the capacitor, and the capacitor is then mounted on a printed circuit board together with a memory device by soldering. Conventionally, soldering to the printed circuit board had been realized by using a solder iron, however, with the recent demand on miniaturized devices or on devices with higher function, there is a requirement to increase the number of electronic components to be mounted in a same area of a printed circuit board. Accordingly, more difficulties are found to obtain a space for inserting the solder iron. Furthermore, to reduce the cost, automated soldering operation is required.
Thus, recently employed are a method comprising mounting the components on the printed circuit board the portions of which are previously coated with a solder cream and the like, or a method comprising mounting the components and then supplying small solder balls thereto. In both methods, the printed board having the components mounted thereon is passed through a heating furnace provided with a high temperature atmosphere set at a temperature not lower than the melting point of the solder, for instance, in a temperature range of from 200 to 260xc2x0 C., such that the solder may be molten to effect the soldering (this method is referred to hereinafter as xe2x80x9creflow solderingxe2x80x9d).
3. Problems that the Invention is to Solve
A coin (button)-type electric double layer capacitor mountable by reflow soldering utilizes an organic solvent for the electrolyte, a metallic oxide for the positive electrode, and a negative electrode having added thereto lithium in some form during the production process to provide the active material. In such a capacitor, the constituents incorporated therein are active by nature of the capacitor itself. Accordingly, if the quantity ratio of the constituents should change depending on the fluctuation in the production process, such a change could cause bulging, liquid leakage (i.e., leaking of the electrolyte to the outside of the capacitor), etc., during the reflow soldering utilized in mounting the capacitor to the product board.
Furthermore, an electric double layer capacitor mountable by reflow soldering must assure the capacitor performance after reflow soldering. However, there are some cases in which the capacitor contains somewhat large amount of foreign matter (i.e., water, etc.). The capacitor characteristics are not influenced at the room temperature, but after reflow soldering or after storage, a sudden deterioration in capacitor characteristics was sometimes found to occur in such cases.
As a means of overcoming the aforementioned problems, the present invention according to a first aspect provides, in a method for producing an electric double layer capacitor comprising a positive electrode, a negative electrode, a non-aqueous solvent, an electrolyte containing a supporting salt, a separator, and a gasket, a method comprising: a step of assembling by caulk sealing inside an electric double layer capacitor said positive electrode, said negative electrode, said non-aqueous solvent, said electrolyte, said separator, and said gasket; and a heating step. In this aspect, an outer connection terminal may be welded after the heating. The heating temperature can be set in a range of from 180 to 300xc2x0C. However, the upper limit of the temperature must be set at a temperature not higher than the melting point of the material constituting the gasket used in the product.
In accordance with a second aspect of the present invention, there is provided, in a mounting method comprising arranging an electric double layer capacitor on a circuit substrate, a mounting method which comprises a step of assembling by caulk sealing inside an inner electric double layer capacitor said positive electrode, said negative electrode, said non-aqueous solvent, said electrolyte, said separator, and said gasket; a heating step; and a step of arranging and reflow soldering said electric double layer capacitor on said circuit substrate. In this case, an outer connection terminal may be welded after the assemblage. Furthermore, preferably, in the heating region of from 0 to 150xc2x0 C., the difference between the temperature profile with respect to time during said heating step and the temperature profile with respect to time during said reflow soldering falls within xc2x150%.
Also preferably, in the heating region of from 0 to 150xc2x0C., the difference in time duration between the time of said heating step and the time of said reflow soldering falls within
It is also preferred that, in the heating region of from 150 to 180xc2x0 C., the difference between the temperature profile with respect to time during said heating step and the temperature profile with respect to time during said reflow soldering falls within xc2x120%.
Further preferably, in the heating region of from 150 to 180xc2x0 C., the difference in time duration between the time of said heating step and the time of said reflow soldering falls within xc2x120%.
Also preferably, in the heating region of from 180 to 300xc2x0 C., the difference between the temperature profile with respect to time during said heating step and the temperature profile with respect to time during said reflow soldering falls within xc2x110%.
It is also preferred that, in the heating region of from 180 to 300xc2x0 C., the difference in time duration between the time of said heating step and the time of said reflow soldering falls within xc2x110%.
In accordance with another aspect of the present invention, there is used a sealing material for an electric double layer capacitor comprising a rubber based adhesive provided with asphalt on the surface thereof. Preferably, the sealing material is provided on the surface of said rubber based adhesive in a plurality of spots set apart from each other.
Also preferably, said asphalt is a fraction obtained by heating crude oil. Furthermore, it is preferred that the rubber based adhesive contains asphalt inside thereof.
Further preferably, the asphalt accounts for 1% or more but not more than 50% of said rubber based adhesive. More preferably, the asphalt accounts for 5% or more but not more than 20% of said rubber based adhesive.
It is also preferred that the asphalt is a blown asphalt or a straight asphalt.
Suitably used as the rubber based adhesive is such based on butyl rubber.
According to a still other aspect according to the present invention, there is used a sealing material for an electric double layer capacitor obtained by mixing asphalt with a rubber based adhesive and by then heating the resulting mixture.
Furthermore according to another aspect of the present invention, there is employed a method for producing a sealing material for an electric double layer capacitor, which comprises mixing asphalt with a rubber based adhesive, and by then heating the resulting product. Preferably, rubber based adhesive is based on butyl rubber. Furthermore, the mixing is carried out in an organic solvent. It is further preferred that the organic solvent is toluene.
In accordance with an aspect of the present invention, there is provided a method for producing an electric double layer capacitor, which comprises: a step of assembling by caulk sealing inside an electric double layer capacitor a positive electrode, a negative electrode, a non-aqueous solvent, an electrolyte, a separator, and a gasket, comprising dissolving a rubber based adhesive and an asphalt in an organic solvent, applying the resulting product to the inner plane of a positive electrode canister and the plane in contact with the negative electrode of the gasket, and drying the coated product; and a heating step. In this case, the asphalt used is straight asphalt. Furthermore, the drying temperature is preferably, 80xc2x0 C. or higher.
Also usable as the asphalt is blown asphalt. In this case, the drying temperature is preferably, 100xc2x0 C. or higher.
Further, by forming a mark showing the heating treatment on the face of the capacitor canister, distinguishable are a final molded product and an intermediate product.
In a still other aspect of the present invention, there is provided, in an electric double layer capacitor comprising a positive electrode, a negative electrode, a non-aqueous solvent, an electrolyte containing a supporting salt, a separator, a gasket, and an external connection terminal, an electric double layer capacitor comprising a mark showing that the product is once heated during its production process.
According to a yet other aspect of the present invention, there is provided an electric double layer capacitor comprising a positive electrode, a negative electrode, a non-aqueous solvent, an electrolyte containing a supporting salt, a separator, and a gasket, which is heated to substantially the temperature of reflow treatment.
In order to achieve the aforementioned objects in the present invention, in the production of a reflow-soldering mountable electric double layer capacitor, the capacitor was subjected to a heat treatment following a temperature profile resembling to the temperature profile with respect to time employed in the reflow soldering step after assembling the electric double layer capacitor. Then, the capacitor characteristics and the appearance were inspected, and those having no anomalies in quality were marked with the product serial number and a symbol of xe2x80x9cHxe2x80x9dto show that the product was subjected to heat treatment. A terminal was welded to the product thereafter.
Although the heat treatment is effective after welding the terminal, considerations should be made on the adhesion to the vessel with heating in case solder plated terminals are used.